In this inaugural year of the Core, we commissioned the three large-size whole-room indirect calorimetry suites which were custom-built for 24-hr energy expenditure studies. To meet the needs of different study designs, the critical needs for these suites are measurement accuracy (between individuals), reproducibility (within individuals), comparability (between suites), and sensitivity (between time intervals). In the past year, we have successfully accomplished first two criteria, as such, two active protocols are using the suites regularly (07-DK-0077 and 07-DK-0202). We have laid the groundwork for further improvements of the suites in the areas of calibration, optimization of new algorithms, and stability, which will take place this coming year. Several new protocols will also be implemented in the metabolic suites. In addition, our efforts in the area of accelerometer development and validation are continuing. We now use these monitors to enhance our field meaurements of physical activity and energy expenditure.